Organic electro-luminescence device

ABSTRACT

An organic electro-luminescence device includes a substrate, a hole injection layer disposed on the substrate, an organic layer disposed on the hole injection layer, a buffer layer disposed on the organic layer, and an electron injection layer forming above the buffer layer. The buffer layer is needed for protecting the organic layer while the electron injection layer is being formed. Within, the organic layer includes a light-emitting layer and an electron transporting layer disposed on the light-emitting layer. The electron transporting layer includes Cesium fluoride.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates generally to organic electro-luminescencedevices (OLEDs) and particularly to a top-emission organicelectro-luminescence device.

(2) Description of the Prior Art

Organic electro-luminescence devices become popular in displaytechnology these days. Comparing to another popular display—liquidcrystal display (LCD), the organic electro-luminescence devices have theadvantage of self light-emitting. Hence, backlight module is no moreneeded in a panel display applied OLEDs.

Please refer to FIG. 1, which is a cross-section view of the structureof an organic electro-luminescence device. The electro-luminescencedevice 100 comprises, in the sequence from bottom to top, a substrate102, a hole injection layer 104, a hole transport layer 110, alight-emitting layer 120, an electron transporting layer 140, and anelectron injection layer 150. Wherein the hole transport layer 110, thelight-emitting layer 120, and the electron transporting layer 140 aremade of organic materials and fabricated via organic processes.

Combination of electron and hole in the light-emitting layer 120 wouldrelease photons. In the process, electrical energy is converted tooptical energy. As shown in FIG. 1, the generated light leaves theelectro-luminescence device 100 through its bottom (the substrate 102).So the electro-luminescence device 100 is also named as an“bottom-emission type”. Wherein, the hole injection layer 104 is usuallymade of ITO material, which is know as a light-transparent material. Theelectron injection layer 150 is made of light-reflecting metal materialswith low work function, for instance, Al, Ca, Mg, and Ag are wellsuited. The light-reflecting character of above materials forces thegenerated light leave the organic electro-luminescence device 100 viathe substrate 102.

However, some essential wires are disposed on the substrate 102. As toan active-matrix organic light emitting display (AM OLED), it even needsthin film transistors (TFTs) array on the substrate 102. Said wires orTFTs would restrict the light utilizing efficiency because of a limitedaperture ratio.

Please refer to FIG. 2. A prior “top-emission type” organicelectro-luminescence device 100 a is presented. Wherein, the generatedlight leaves the organic electro-luminescence device 100 a via theelectron injection layer 150. In this case, the electron injection layer150 should be made of light transparent materials, usually ITO, which isalso conductive. Because the needed wires or TFTs are made on thesubstrate 102, no aperture ratio issue should be concerned in thetop-emission type organic electro-luminescence device 100 a. Comparingto the organic electro-luminescence device 100 of FIG. 1, the organicelectro-luminescence device 100 a could provide a better light utilizingefficiency.

While applying conductive transparent material like ITO for the electroninjection layer 150, a major issue is that sputtering process of the ITOmaterial would damage the organic materials (140) beneath. Please referto FIG. 2, a buffer layer 145 made of CuPc is therefore provided by G.Parthasaraty et al. Before forming the electron injection layer 150, thebuffer 145 is formed firstly to withstand the sputtering process.However, while practical estimated, the electron injection efficiency ofthe organic electro-luminescence device 100 a is too poor to apply incommercial application. An experiment data shows that the organicelectro-luminescence device 100 a according to G. Parthasaraty et al.has an electron injection efficiency of 3.7 mA/cm² with a workingvoltage at 6 V, mean while, the energy efficiency is less than 1 lm/W.

Please refer to FIG. 3. Another prior organic electro-luminescencedevice 100 b provided by Hung Liang-sun et al. is presented. Beforesputtering the buffer layer 145, a LiF/AL interface layer 143 [thicknessof AL is about 10˜20 A], which is a thin metal layer, is sputteredfirstly. Wherein, the buffer layer 145 still comprises CuPc compound.Diffusion of Li from the LiF/AL interface layer 143 to the underneathorganic materials (140) could lower the energy barrier of Al chelate inthe electron transporting layer 140. From this view, Hung Liang-sun etal. seems have been solved the problem of the organicelectro-luminescence device 100 a taught by G. Parthasaraty et al.

However, please still refer to FIG. 3, Li of the LiF/AL interface layer143 could further diffuse into the light-emitting layer 120. This maydecrease the life time of the organic electro-luminescence device.Furthermore, the light-emitting layer 120, the electron transportinglayer 140, and the buffer layer 145 is fabricated in organic chamber,but the LiF/AL interface layer 143 is fabricated in a metal chamber.Hence the fabrication process of the organic electro-luminescence device100 b comprises moving to the metal chamber after forming thelight-emitting layer 120 and the electron transporting layer 140 in aorganic chamber, then moving to a organic chamber, finally moving to asputtering chamber to from the electron injection layer 150. Thecomplicated process (at least three times of movement between differentchambers) is a disadvantage of organic electro-luminescence device 100b.

Therefore, how to provide a top-emission organic electro-luminescencedevice, which overcomes the mentioned problems—the damage of sputteringprocess, the low electron injection efficiency, the decreased life timeof organic materials and the complicated fabrication process, is themajor issue of the present invention.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an organicelectro-luminescence device with high electron injection efficiency.

It is another object of the present invention to solve the priordisadvantage of decreased life time of organic materials.

It is another object of the present invention to provide a method forfabricating an organic electro-luminescence device without complicatedprocess.

The present invention relates to an organic electro-luminescence deviceincluding a substrate, a hole injection layer disposed on the substrate,an organic layer disposed on the hole injection layer, a buffer layerdisposed on the organic layer, and an electron injection layer formingabove the buffer layer. The buffer layer is needed for protecting theorganic layer while the electron injection layer is being formed.Within, the organic layer at least includes a light-emitting layer, andan electron transporting layer disposed on the light-emitting layer. Theelectron transporting layer at least includes cesium fluoride to loweran energy barrier.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment which isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be specified with reference to itspreferred embodiment illustrated in the drawings, in which:

FIG. 1 shows a cross section view of an bottom-emission type organicelectro-luminescence device in accordance with a prior art;

FIG. 2 shows a cross section view of a top-emission type organicelectro-luminescence device in accordance with a prior art;

FIG. 3 shows another cross section view of a top-emission type organicelectro-luminescence device in accordance with another prior art; and

FIG. 4 shows a cross section view of the organic electro-luminescencedevice of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention aims at providing an organic electro-luminescence devicesand particularly to a top-emission organic electro-luminescence device,which has high current injection efficiency, relatively loner life time,and can be fabricated with relatively simplified processes.

Please refer to FIG. 4, which is a cross section view of an organicelectro-luminescence device of the present invention. While fabricatingthe organic electro-luminescence device 200, a substrate 202 is providedfirst, then a hole injection layer 204 is disposed on the substrate 202.In one embodiment, the substrate 202 is made of light transparentmaterials or opaque materials with light reflection character. The holeinjection layer 204 is made of conductive transparent materials (forinstance, ITO, IZO) via sputtering process.

Next, an organic layer 23 is disposed on the hole injection layer 204.Wherein the organic layer 23 is an multi-layer structure. It at leastcomprises a light-emitting layer 220 and a electron transporting layer240. The electron transporting layer 240 is disposed on thelight-emitting layer 220. The electron transporting layer 240 includesCesium fluoride. The organic layer 23 further comprises a hole transportlayer 210 between the light-emitting layer 220 and the hole injectionlayer 204.

The material of the light-emitting layer 220 is selected from the groupof fluorescent dyes, phosphorous dyes, or chelate materials. Forinstance, materials selected from the group of Alq3

NPB

CuPc

C545T

DCJTB

CBP

Balq

Ir(ppy)3 are applied in separated embodiments of the present invention.The method for forming the light-emitting layer 220 is select fromvacuum sputtering, plasma polymerization, vacuum evaporating, spincoating, dip coating, Langmuir-Blodgett Film tech., Sol-Gel tech.,electrolytic polymerization.

Afterwards, the electron transporting layer 240 is disposed on thelight-emitting layer 220. The method of fabricating the electrontransporting layer 240 comprises the following steps, in sequence: (1)disposing a metal chelate material above the light source 220 and (2)doping a CsF compound into the metal chelate material. Wherein the metalchelate material is an aluminum chelate (Alq3), and the doping processis via thermal evaporation.

The doping process of CsF is an partially doping process. Only the topportion of the electron transporting layer 240 is doped with CsF. Theother portion of the electron transporting layer 240 is undoped. So theelectron transporting layer 240 is a double-layer structure. In FIG. 4,the electron transporting layer 240 comprises a first electrontransporting layer 241 and a second electron transporting layer 242. Thesecond electron transporting layer 242 is positioned above the firstelectron transporting layer 241. The second electron transporting layer242 comprises the CsF compound and the metal chelate material. The firstelectron transporting layer 241 comprises the metal chelate material,for instance, the aluminum chelate.

A buffer layer 245 is disposed on the organic layer 23. Wherein, thebuffer layer 245 includes a phthalocyanine-based organic compound, forinstance, phthalocyanine-Cu complex. All the above processes (fromforming the organic layer 23 to the forming of the buffer layer 245) isable to be accomplished in an organic chamber. Even the forming processof the electron transporting layer 240 is accomplished in the sameorganic chamber. Hence, no chamber-transferring is needed during theseprocesses.

Lastly, the electron injection layer 250 is disposed on the buffer layer245. The electron injection layer 250 is made of conductive transparentmaterials, such as ITO or IZO, via a high energy sputtering process. Onefunction of the buffer layer 245 is to protect the underneath layersfrom the damage aroused from the high energy sputtering process.

According to the above description, the present fabrication method ofthe organic electro-luminescence device 200 is much simpler than thementioned prior arts. According to the teaching of Hung Liang-sun etal., three times of chamber transferring are needed after forming thelight-emitting layer (organic chamber→metal chamber→organicchamber→sputtering chamber). But the processes of the present inventionare able to be accomplished in the organic chamber from the formingprocess of the light-emitting layer 120 to the forming process of thebuffer layer 245. Only one chamber transferring is needed at the formingprocess of the electron injection layer 250, which is in the sputteringchamber. Hence, the drawback of complicated process of mentioned priorarts is removed.

An experimental data via the present invention shows that the organicelectro-luminescence device 200 has an electron injection efficiency of52 mA/cm² with a working voltage at 6 V. Obviously, the efficiency ismuch better than the mentioned prior arts according to G. Parthasaratyet al. and Hung Liang-sun et al. Mean while, the energy efficiency ofthe present invention is about 11.6 lm/W, which also overcomes thementioned prior arts (1 lm/W for G. Parthasaraty et al. and 9 lm/W forHung Liang-sun et al.).

Furthermore, the life time of the organic electro-luminescence device200 is longer than 1500 hours with a brightness of 2000 nits. Clearly,the disadvantage of decreased life time due by diffusion of Li isimproved in the present invention. The present organicelectro-luminescence device has a relatively longer life time.

As can be understood by a person skilled in the art, the foregoingpreferred embodiment of the present invention is illustrated of thepresent invention rather than limiting of the present invention. It isintended to cover various modifications and similar arrangementsincluded within the spirit and scope of the appended claims, the scopeof which should be accorded the broadest interpretation so as toencompass all such modifications and similar structure.

While the present invention has been particularly shown and describedwith reference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may bewithout departing from the spirit and scope of the present invention.

1. An organic electro-luminescence device comprises: a substrate; a holeinjection layer disposed on the substrate; an organic layer, disposed onthe hole injection layer, having a light-emitting layer and an electrontransporting layer disposed on the light-emitting layer, wherein theelectron transporting layer comprises cesium fluoride; a buffer layerdisposed on the organic layer; and an electron injection layer disposedon the buffer layer.
 2. The organic electro-luminescence deviceaccording to claim 1, wherein the electron transporting layer comprisesa metal chelate compound.
 3. The organic electro-luminescence deviceaccording to claim 2, wherein the metal chelate compound comprises analuminum chelate.
 4. The organic electro-luminescence device accordingto claim 1, wherein the electron transporting layer comprises a firstelectron transporting layer and a second electron transporting layercomprising cesium fluoride.
 5. The organic electro-luminescence deviceaccording to claim 4, wherein the second electron transporting layercomprises a metal chelate compound.
 6. The organic electro-luminescencedevice according to claim 5, wherein the metal chelate compoundcomprises an aluminum chelate.
 7. The organic electro-luminescencedevice according to claim 4, wherein the first electron transportinglayer comprises a metal chelate compound.
 8. The organicelectro-luminescence device according to claim 7, wherein the metalchelate compound comprises an aluminum chelate.
 9. The organicelectro-luminescence device according to claim 1, wherein the bufferlayer comprises a phthalocyanine-based organic compound.
 10. The organicelectro-luminescence device according to claim 1, wherein the bufferlayer comprises copper phthalocyanine (CuPc).
 11. The organicelectro-luminescence device according to claim 1, wherein the organiclayer further has a hole transporting layer disposed under thelight-emitting layer.